1. Field of the Invention
The invention relates to a mobile crane with a chassis bearing the revolving superstructure having a jib and counter-jib, which is detachably connected to lateral crawlers.
2. Description of the Related Art
Mobile cranes are generally provided with crawler tracks instead of wheels if the crane is travelled on the construction site with equipment and ballast and possibly with load. If the undercarriage comprises a chassis connected to crawlers, the stabilisation area of the crawler-mounted crane is determined by the rear-end tread rollers of the crawlers which define a rectangular stabilisation area. The revolving superstructure pivoted on the undercarriage carries the jib, which can be a telescoping jib, and a counter-jib which bears a counter-ballast.
If the jib is luffed, the effective stabilisation area under the crawler tracks can change. If, in such a case with a crawler-mounted crane, the centre of gravity migrates due to the luffing of the jib or the taking up of load in the direction of one end of the crawlers, the stabilisation area becomes smaller to the degree in which the centre of gravity migrates towards one crawler track end. The subgrade reaction increases accordingly, which can lead to a failure of the ground contact area (shear failure), whereby the crane can overturn.
A particular problem occurs if the jib takes up a steep position without load as then the crawler-mounted crane can overturn backwards due to the counterweight at the revolving superstructure. To prevent such a turning over with a steeply positioned jib, the crawler must be ballasted accordingly, for which purpose, for example, additional weights of up to 100 t can be required whose necessity means increased effort. The additional weights not only make additional transport necessary, but also an increased effort in assembly.
It is therefore the object of the invention to provide a crawler-mounted crane of the kind first given which has a favourable stabilisation area so that the problem of counter-ballasting does not result even with a steeply positioned jib.
It is another object of the invention to achieve an increase in the stabilisation base, on the one hand to allow high loads to be hoisted with large jib radii and low ballast and, on the other hand, to allow the raising of long jib systems.
It is another object of the invention to allow the crane to be aligned horizontally even with an uneven contact area.
These objects are solved in accordance with the invention by cantilevering stabilisers being attachable to the outsides of the crawlers.
With the crawler-mounted crane in accordance with the invention, essentially only the cantilevering stabilisers define the rectangular or square stabilisation area so that the size of the effective stabilisation area generally does not change even when the centre of gravity migrates in the direction of an overturn edge. If the stabiliser bases disposed on the stabilisers define the standard rectangle, under strain an increased consolidation occurs under the stabilisers which, however, only leads to a slight shift in the centre of gravity. The stabilisation area under the stabilising cylinders remains constant.
Appropriately, brackets can be pinned or otherwise connected to the crawlers, which brackets bear two cantilevering stabilisers each. Appropriately, vertical hydraulic cylinders are fastened to the ends of the stabilisers with whose aid the crane can be aligned horizontally even with uneven ground.
In another aspect of the invention, it is provided that the stabilisers are swivellably supported on the brackets. This embodiment does not only allow an adjustment of the rectangular stabilisation area, but also permits the alignment of the stabilisers in line with the bracket so that they can be laid down in their extended form for their transport on a transport vehicle such as a low-bed trailer. If the stabilisers are fixedly connected to the bracket in trapezoid form, they cannot be transported in a space-saving manner so that it can be necessary to provide a special transport vehicle for each stabiliser pair with bracket.
Appropriately, the stabilisers can be telescoped out to reduce the transport dimensions and, when little space is available, to reduce the required stabilisation area.
According to another further development of the invention, it is provided that the stabilisers can be directly pinned or connected in another manner to the chassis after the crawlers have been removed. In this way, the undercarriage can be designed as a portal with good stability properties. The transportation and assembly of the crawlers can be dispensed with in this case.
The stabilisers can also be connected to the chassis by the interposing of intermediate brackets so that in this way, the size of the stabilisation area or of the positional rectangle can be additionally increased.